The 800 series phones are pretty robust. However sometimes if the phone is dropped it can knock the bells out of adjustment. In most cases it is easy to fix, sometimes however it needs a replacement.

In the above picture to adjust the bell you unscrew one screw at a time of the bell. You find once the screw is loose you can spin the bell. The bell is not symmetrical and when you spin it you change the distance between the bell striker and the bell. If the bell is striking properly you can adjust it closer - or further away. When you have finished tighten up the screw.

Sometimes the Bell actuator comes loose. There are two screws that attach the actuator to the base. You can loosen the screws and move the actuator to adjust how the Bell striker hits the Bells. In extreme cases if the phone is dropped the tabs can break off the Bell actuator, and the only solution is a replacement